1. Field of the Invention
The present invention relates to a filter device for removing impurities, such as residual chlorine, from city water or like. Particularly, it relates to a filter device having means for preventing reduction of filtering area due to deformation of filter element. The present invention provides an improvement in structure of the filter element adapted to be used with a powdered absorbent which adheres onto the surface of the filter element to form a pre-coat layer so that the adhering pre-coat layer is retained evenly during the filtering operation and retained permanently for an extended time period.
2. Prior Art Statement
City water generally contains residual chlorine or other impurities which provide unpleasant ordor or taste. In order to remove such impurities, it is a common practice to filter city water to remove such impurities by the use of a filter device in which an absorbent, such as activated carbon, is contained.
Examples of known filter device of this type are disclosed in Unexamined Japanese Utility Model Publication Nos. 16739/1975 and 100367/1975, wherein a filter cloth is formed to be in a pouch which is folded and contained in a casing, and activated carbon powder particles are filled in the casing to surround the pouch. As water is introduced initially into the filter device, the activated carbon powder particles adhere to the surface of the pouch to form a pre-coat layer. In the filter device of this type, city water is cleaned by the filtering action of the filter cloth and impurities contained therein are absorbed by activated carbon powder particles forming the pre-coat layer.
However, since the filter cloth in the known filter device is simply folded and contained in the casing not to be firmly retained to keep its shape, the shape of the folded filter cloth is changed due to change in pressure of the flowing water caused by repeated operations of initiating and terminating the passage of water or due to increase in pressure caused by clogging of water, leading to reduction of the filtering area.
The known filter device has further disadvantages that the pre-coat layer cannot be formed evenly over the entire surface area of the filter cloth and that the formed pre-coat layer tends to be cracked or otherwise damaged.
The aforementioned disadvantages of the known filter device is lead from the fact that the shape of the filter cloth pouch is not firmly retained to make it impossible to provide uniform gaps between the adjacent pleats of the folded filter cloth and also between the filter cloth and the inner surface of the casing so that activated carbon particles cannot adhere evenly to the surface of the filter cloth to form the pre-coat layer of uniform thickness. Furthermore, no pre-coat layer is formed on the portions at which adjacent pleats of filter cloth contact with each other, or the pleat of the filter cloth contacts with the surface of the casing, to leave the uncoated filter cloth.
Since the filter cloth is not retained to hold its shape, as described above, and simply folded into an irregular shape, fine wrinkles are formed on the filter cloth. These fine wrinkles ruffle frequently as the water pressure is changed by the initiation and termination of water supply to cause cracking of the pre-coat layer adhering onto the surface of the filter cloth. Accordingly, the pre-coat layer formed on the surface of the filter cloth cannot be retained permanently.